Conventionally various treatments, examinations, and procedures have been carried out by inserting a medical instrument such as a catheter into a tubular organ of a human body such as a blood vessel, a digestive tract, or a urinary duct. In addition, recently a medicinal-liquid injection apparatus such as a medicinal-liquid injection catheter has been used to carry out a treatment or a procedure of injecting an appropriate medicinal liquid to a lesion of a body tissue of a living being (see, e.g., Patent Documents 1 and 2).
As is well known in the art, the medicinal-liquid injection catheter includes a tubular main body having a lumen therein, and a needle-like tubular member that is constituted by a thin tube in which a medicinal liquid can flow, that includes an acuminate needle portion as a free end portion thereof, and that is inserted in the lumen so as to be movable in an axial direction of the main body. The main body of the medicinal-liquid injection catheter is inserted in a blood vessel so as to reach a lesion of a body tissue, and therein the needle-like tubular member is moved in a lengthwise direction thereof. Thus, through a hole formed in an end opening portion or a tubular wall of the catheter main body, the needle portion as the free end portion of the needle-like tubular member is caused to project out of the lumen into an outside space, so as to puncture the lesion of the body tissue. In this state, the medicinal liquid is injected to the lesion through the needle-like tubular member.
Meanwhile, when the catheter main body of the medicinal-liquid injection catheter is inserted in, e.g., the blood vessel as described above, some portions of the catheter main body are bent or curved in the winding blood vessel. Therefore, when the needle-like tubular member is inserted in the lumen of the catheter main body and is moved in the axial direction of the catheter main body, the tip of the needle portion of the needle-like tubular member may contact an inner circumferential surface of the lumen to be lodged therein. In this case, the needle-like tubular member may not be moved smoothly in the lumen, and also the inner surface of the lumen may be damaged.
Generally, the needle-like tubular member is long, and the lumen of the main body has an inner diameter greater than an outer diameter of the needle-like tubular member by a certain amount so as to allow the needle-like tubular member to be sufficiently inserted therein. Thus, in the conventional medicinal-liquid injection apparatus such as the medicinal-liquid injection catheter, the needle-like tubular member may be deflected when the needle-like tubular member is moved in the lumen, therefore it is difficult to cause the needle portion of the needle-like tubular member to project stably in a desired direction out of the hole through which the lumen opens outward.    Patent Document 1: Japanese Patent Application Publication No. 2001-104487    Patent Document 2: Japanese Patent Application Publication No. 2001-299927